rusk

1. A rectangular, hard, dry biscuit. (countable, uncountable)
2. A twice-baked bread, slices of bread baked until they are hard and crisp; zwieback. (countable, uncountable)
3. A weaning food for children. (countable, uncountable)
4. A cereal binder used in meat product manufacture. (countable, uncountable)

Plural rusks